This study will evaluate the efficacy and safety of inavolisib in combination with Phesgo (pertuzumab, trastuzumab, and rHuPH20 injection for subcutaneous use) compared with placebo in combination with Phesgo, as maintenance therapy, after induction therapy in participants with previously untreated HER2-positive advanced breast cancer (ABC).
Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1
Histologically or cytologically confirmed and documented adenocarcinoma of the breast with metastatic or locally advanced disease not amenable to curative resection
Confirmation of HER2 biomarker eligibility based on valid results from central testing of tumor tissue documenting HER2-positivity
Confirmation of PIK3CA-mutation biomarker eligibility based on valid results from central testing of tumor tissue documenting PIK3CA-mutated tumor status
Prior treatment in the locally advanced or metastatic setting with any PI3K, AKT, or mTOR inhibitor or any agent whose mechanism of action is to inhibit the PI3K-AKT-mTOR pathway
Any prior systemic non-hormonal anti-cancer therapy for locally advanced or metastatic HER2-positive breast cancer prior to initiation of induction therapy
History or active inflammatory bowel disease
Disease progression within 6 months of receiving any HER2-targeted therapy